Description: High blood pressure, or hypertension , is defined in an adult as a systolic pressure of 140 millimeters of mercury, or higher, and/or a diastolic pressure of 90 millimeters of mercury, or higher.

Symptoms: High blood pressure usually has no specific symptoms and no early warning signs. It's known as a "silent killer" but can be detected by a simple, quick and painless test.

Number of Americans diagnosed: About 50 million Americans aged 6 and older have high blood pressure.